Oi, formerly known as Telemar, is the largest fixed telephone operator and the fourth mobile telephone operator in Brazil, being the third largest telecommunication company in Latin America. It is headquartered in Rio de Janeiro. In 2013, Oi announced its merger with Portugal Telecom, the largest telecommunication company in Portugal. In June 2015, Portugal Telecom was acquired by Altice Group. On June 20, 2016, Oi filed for a US$19 billion bankruptcy protection, the largest on record for Brazil. Wikipedia